Cryptorchidism is defined as the absence of one or both testicles from the scrotum, and the incidence of congenital cryptorchidism in full-term males is estimated at 2% to 4%.⁷ Testicles originate in the high retroperitoneum; therefore, ultrasound evaluation for undescended testicles must extend from below the liver and spleen, inferiorly through retroperitoneum and inguinal canals, to the scrotum (Fig. 18.4). Multiple risk factors have been implicated for causing undescended testicles, including prematurity and multiple maternal factors/exposures; however, no single etiology stands out.⁸,⁹,¹⁰

If undescended testicles are occult to ultrasound, MRI may be helpful, particularly using T2-weighted and diffusion-weighted sequences where they appear hyperintense (Fig. 18.4). The undescended testicle has a higher risk of malignancy (especially seminoma), and it is unclear whether this risk is decreased with surgical repair.¹¹

Ambiguous external genitalia can be a source of great concern and require a multidisciplinary approach to determine the correct diagnosis. The currently accepted term for the spectrum of etiologies is “disorders of sex development” (DSD). It should be noted that not all DSD manifests as ambiguous external genitalia. In the absence of the Y chromosome, the internal and external genitalia develop the “default” female phenotype.

Ultrasound workup of ambiguous genitalia must include evaluation of scrotum/labia, inguinal canals, pelvis, kidneys, and adrenal glands. As shown in Table 18.1, identification of the uterus and characterization of both gonads are critical to classifying the DSD. The most common cause of ambiguous genitalia is congenital adrenal hyperplasia, which is one of the several causes of female pseudohermaphroditism (46,XX).¹² In congenital adrenal hyperplasia, the adrenal glands are often enlarged with a “cerebriform” appearance. The most common cause of ambiguous genitalia with a 46,XX genotype is androgen insensitivity syndrome, which is one of the several causes of male pseudohermaphroditism.¹² In complete androgen insensitivity (Fig. 18.4), the external genitalia are female, whereas in partial androgen insensitivity, the external genitalia are ambiguous. In some children, DSD may be very complex, requiring MRI evaluation and a systematic interdisciplinary approach to fully classify and characterize the disorder (Fig. 18.5).

Heterotopic adrenal cortical tissue can be found in the paratesticular region and sometimes within the testicle. Intratesticular adrenocortical tissue can proliferate into tumor-like masses in patients with congenital adrenal hyperplasia, and Nelson syndrome can sometimes present with detectable intratesticular masses at ultrasound both during childhood and adulthood.¹³,¹⁴,¹⁵ The adrenal tissue becomes trapped in the testicles in utero prior to migration from the high retroperitoneum and subsequently enlarges in response to elevated adrenocorticotropic hormone.
Although their ultrasound appearance can be variable, these rests most often present as one or more bilateral intratesticular hypoechoic masses (Fig. 18.6).¹³ Testicular venous sampling for elevated cortisol levels may confirm the diagnosis.¹⁶

Splenogonadal fusion is a rare cause of an extratesticular mass that results from the migration of splenic tissue with the testicle.¹⁷ The connection may be direct (continuous) with the principle spleen fused to the intrascrotal testicle or indirect (discontinuous) with independent (ectopic) splenic tissue traveling into the scrotum with the testicle. Although the involved splenic tissue should have similar imaging features of native spleen at ultrasound, CT, and MRI (Fig. 18.7), there may be overlap in appearance with the testicle. Although scintigraphy (^99mTclabeled sulfur colloid or damaged red blood cells) could potentially help in the diagnosis,¹⁸ splenogonadal fusion is rare; therefore, most patients go on to surgery for removal of a scrotal mass and the diagnosis is confirmed by histopathology.

Tunica albuginea cysts are common benign palpable avascular cysts that arise from the tunica albuginea, the fibrous capsule surrounding the testicle. Uncomplicated cysts are anechoic at ultrasound and may exert mass effect on the underlying testicular parenchyma (Fig. 18.8). Complicated cysts may contain debris or calcification. The location of this type of cyst is key to distinguishing it from other cystic abnormalities arising from either the testicle or epididymis.¹⁹

If the processus (tunica) vaginalis completely envelopes the testicle and there is failure of normal posterior anchoring of the testicle to the scrotum, the resulting configuration is called a “bell clapper” anomaly. This is because the testicle can freely swing and rotate within the processus vaginalis like a bell clapper in a bell (Fig. 18.9). Normally, a broad base of direct testicular contact with the internal spermatic fascia prevents free mobility. Therefore, children with a bell clapper anomaly are at increased risk of intravaginal testicular torsion.²⁰ The incidence of bell clapper anomaly has been reported to be 12% in autopsy series,²¹ although the frequency of torsion is far less than this²²; therefore; other factors are likely involved.

Testicular torsion is the twisting of the testicle about the spermatic cord and causes obstructed venous outflow, lack of arterial inflow, and eventual infarction of the testicle (Fig. 18.10). The clinical presentation is most often severe acute unilateral scrotal pain, nausea, and vomiting; physical exam may reveal a high-riding horizontal testicle with an absent cremasteric reflex.²³ The acute presentation should help distinguish torsion from the gradual symptom onset of epididymitis or orchitis; however, intermittent torsion may present more subacutely.²⁴ The lack of venous outflow leads to testicular congestion (edema), and this presents at ultrasound as an enlarged testicle with decreased echogenicity and heterogeneous echotexture as well as decreased Doppler

blood flow (Fig. 18.11). Prolonged torsion may result in a markedly enlarged, heterogeneous testicle with areas of geographic increased and decreased echogenicity. However, as abnormally decreased Doppler blood flow is only 84% sensitive for detecting torsion, normal or increased intratesticular Doppler signal should not exclude the diagnosis when clinical suspicion is high.²⁵ Presumably, a false-negative Doppler ultrasound examination is commonly due to intermittent torsion.

There are two unique types of testicular torsion that occur in children. As discussed above, the bell clapper anomaly is a developmental abnormality where the testicle is inadequately affixed to the posterior scrotum, thus allowing the spermatic cord and testicle to twist within the confines of the processus (tunica) vaginalis. This type of torsion is therefore defined as intravaginal. The diagnosis of a bell clapper anomaly can be confidently made when fluid completely surrounds the testicle without the usual posterior anchoring of the gubernaculum, epididymis, and testis to the scrotum. The “torsion knot” sign may also be observed, appearing as a supratesticular mass-like abnormality, which is due to twisted, edematous spermatic cord.²⁶ Intravaginal torsion is much more common in adolescents, whereas extravaginal torsion (described below) is more common in neonates.

Very young children (including fetuses and neonates) are susceptible to testicular torsion due to a deficient gubernaculum, which allows the testicle and processus vaginalis to twist together. This type of torsion is referred to as extravaginal, and it most often occurs in utero or soon after birth. At ultrasound, findings suggestive of extravaginal testicular infarction include a small hypoechoic testicle (frequently inguinal in location) with a calcific rim (the rim is echogenic and may show posterior acoustic shadowing) and decreased Doppler blood flow²⁷ (Fig. 18.12).

Treatment of testicular torsion generally requires surgery; however, there is only about a 4- to 8-hour window after onset before permanent ischemic damage occurs. Delay in treatment may result in infertility or require orchiectomy.²³ In cases where a bell clapper anomaly is present, bilateral orchiopexy is performed. Based on a recent survey of practicing urologists, management of neonatal (including prenatal/perinatal) torsion is inconsistent with children undergoing surgical exploration on emergent, urgent, and elective bases.²⁸ In the setting of neonatal torsion (when bell clapper anomaly is not the primary mechanism of torsion), many surgeons also still perform bilateral orchiopexy.²⁸,²⁹

Pediatric patients with infectious or inflammation of the testicle and epididymis may present with severe pain, swelling, and hematuria and/or ejaculation of blood, and presenting signs and symptoms overlap considerably with testicular torsion.²⁵,³⁰,³¹,³²,³³,³⁴ The primary cause of orchitis and epididymitis in young children is an underlying genitourinary tract abnormality (e.g., neurogenic bladder or ectopic ureter), whereas a descending or sexually transmitted urinary tract infection from E. coli, N. gonorrhea, or Chlamydia is more common in adolescents. Viruses, including mumps, are another potential infectious cause.³⁵

Ultrasound can help differentiate between orchitis and testicular torsion. Orchitis frequently shows an enlarged, heterogeneous, hypoechoic testicle with increased color Doppler blood flow³⁰ (Fig. 18.13), whereas torsion most often has absent or decreased Doppler blood flow. Both echotexture and Doppler blood flow can be variable in appearance with epididymo-orchtis, however: the testes and epididymides have normal echotexture and show only hyperemia in 20% of patients with epididymitis and 40% of patients with orchitis.³⁶ An enlarged epididymis in children with testicular torsion may lead to a misdiagnosis of epididymitis in cases of partial or intermittent torsion and normal or increased testicular blood flow.³⁷,³⁸ The sonographic findings of leukemia or lymphoma involving the testicle show considerable overlap with and may be challenging to distinguish from epididymo-orchitis.³⁹ Once other etiologies are excluded, the management of epididymo-orchitis is directed at the suspected organism with antibiotic therapy, hot or cold packs for analgesia, and scrotal elevation.⁴⁰

Increased fluid in the scrotal sac is a common finding on ultrasound and is most often due to a simple hydrocele.³⁰,⁴¹,⁴² Hydroceles are collections of fluid that develop between the visceral and parietal layers of the tunica vaginalis and/or along the spermatic cord, and at ultrasound they typically appear as thin-walled anechoic fluid collections (Fig. 18.14) or fluid collections with low-level swirling echoes⁴³. Children with hydroceles most commonly present with painless scrotal swelling. The etiology is congenital in most neonates and infants as well as some older children, because of a patent processus vaginalis (Fig. 18.15). Hydroceles in older children and adolescents are more likely to be acquired from inflammation/infection, testicular torsion, trauma, or a tumor.³⁰ In rare cases, very large hydroceles may communicate with the abdominal cavity, having an “hour-glass” configuration, and are called abdominoscrotal hydroceles⁴⁴,⁴⁵,⁴⁶ (Fig. 18.16). Spermatic cord hydroceles may be classified into two types: the fluid of an encysted hydrocele does not communicate with the peritoneal cavity above or the scrotal sac below, whereas the fluid of a funicular hydrocele communicates with the peritoneal cavity at the internal ring but not the scrotum.⁴⁷,⁴⁸

Other cystic/fluid-filled abnormalities that may occupy the scrotal sac and inguinal canal include infection (pyocele and scrotal abscess), hematocele (usually due to recent trauma), and bowel from an inguinal hernia (Fig. 18.17). Pyoceles and hematoceles are commonly complex in appearance, containing debris, septations, and fluid-fluid levels at ultrasound.

Torsion of an intrascrotal appendage is a common cause of acute scrotal pain during the pediatric period.⁴⁹ These appendages are embryonic remnants of the paramesonephric (testicular) and mesonephric (epididymis) ducts and are named based on their location.³⁶,⁵⁰ Three of five types can be identified on ultrasound and are more readily apparent in the presence of a hydrocele—the appendix testis, appendix epididymis, and appendix of the epididymal tail.³⁰